Astrophysics > High Energy Astrophysical Phenomena

Title:VLBI and Archival VLA and WSRT Observations of the GRB 030329 Radio Afterglow

Abstract: We present VLBI and archival Karl G. Jansky Very Large Array (VLA) and
Westerbork Synthesis Radio Telescope (WSRT) observations of the radio afterglow
from the gamma-ray burst (GRB) of 2003 March 29 (GRB 030329) taken between 672
and 2032 days after the burst. The EVLA and WSRT data suggest a simple power
law decay in the flux at 5 GHz, with no clear signature of any rebrightening
from the counter jet. We report an unresolved source at day 2032 of size
$1.18\pm0.13$ mas, which we use in conjunction with the expansion rate of the
burst to argue for the presence of a uniform, ISM-like circumburst medium.
We develop a semi-analytic method to model gamma-ray burst afterglows, and
apply it to the 5 GHz light curve to perform burst calorimetry. A limit of $<
0.067$ mas yr$^{-1}$ is placed on the proper motion, supporting the standard
afterglow model for gamma-ray bursts.